Study On The Preparation And Structural Properties Of Zirconium Diboride Ceramic Fibers

Zirconium Diboride(ZrB2)ceramic has wide applications in ultra-high temperature environment of more than 2000? due to its unique combination of high melting temperature of more than 3000?,high hardness,good impact resistance and good conductivity.Many studies concerned the preparation and improvement of ZrB2 powders and bulks,while rarely on ceramic fibers.It will contribute the study of fiber-reinforced composites in ultra-high-temperature environment if we conduct the researching of ZrB2 ceramic fibers,which may overcome the low thermal shock resistance of ceramics and satisfy the country's need.This paper aims to explore the preparation,structure and properties of ZrB2 ceramic fibers.Based on the liquid precursor method for preparing ZrB2 ceramic,ZrB2 precursor spinning solution was obtained after the mixture and concentration of inorganic substances and spinning additive polyvinyl alcohol(PVA),and then ZrB2 ceramic fibers were prepared by sintering the precursor fibers which was produced by the dry spinning technique.The structures and properties of precursor spinning solution,precursor fibers and the resultant ceramic fibers were studied by a series of testing methods,such as rotational rheometer,TGA,DSC,FTIR,GC-MS,SEM,XRD,EA,XPS,etc.The results were as follows.(1)Complicated chemical structures formed owing to the reactions among inorganic compounds and PVA,which resulted in the improved stability of precursor spinning solution as the reaction proceeds.Moreover,the spinning solution was a Non-Newton fluid.The spinning temperature increased when the content of PVA decreased due to the increased viscosity.The preferable spinning temperature was 40-55? and the viscosity of the spinning solution was 100-200Pa·s.(2)The optimal spinning parameters for the dry spinning of precursor fibers were obtained.Continuous precursor fibers with 15?m in diameter were obtained when the take-up speed reached a maximum value of 350m/min.The tensile strength of precursor fibers decreased from 890MPa for the samples with 50%PVA to 460MPa with 25%PVA,while the ceramic yield increased from 12%to 30.9%.(3)The calcination mechanism and optimal calcination procedure were investigated.The results showed that ZrB2 ceramic fibers with pure crystallization structure and 3nm diameter micropores could be obtained after calcination at 1600?,continuous ceramic fibers were also obtained.The diameter of the ceramic fiber was about 13?m and the carbon content was 30.16%.(4)The effects of holding time at calcination temperature 1600 ? and the content of spinning additive on the structures,mechanical properties and antioxidant properties of resultant ceramic fibers were also studied.The results showed that favorable ZrB2 ceramic fibers can be obtained after calcinating the precursor fibers with 35%PVA at 1600? for 3-4 hours.Dense ceramic fiber was obtained with a low carbon content 15.56%and the mechanical strength was 710MPa.The resultant ZrB2 ceramic fibers had excellent high temperature oxidation resistance.It can maintain its weight up to 1400? in nitrogen atmosphere while remain 70%of initial weight in air up to 1400?.In addition,the ZrB2 ceramic fibers were modified by adding Tetraethyl orthosilicate(TEOS).When the Zr:Si=4.5:1(mole ratio),the high temperature oxidation resistance of the ceramic fibers improved while the structure and composition had little changes.